The creation of finished, bound books using “print on-demand” processes and electronic print engines is becoming ever more popular for publishers of all sizes. Unlike traditional printing processes, which employ fixed plate presses to transfer images to the web or sheet, electronic printing allows for the creation of smaller print runs that can be customized, on a book by book basis. To maximize efficiency, pages for finished books are often printed on a larger overall web or sheet, which is subsequently cut and slit into the desired page dimensions. These cut pages are thereafter fed to a collection point and stacked into finished “book blocks.” The book blocks are trimmed into squared-off stacks using a three-knife trimmer, and directed to a binding process, wherein an outer cover is bound to the book page stack.
The creation of book blocks often involves a number of manual steps. For example, printers often generate a plurality of page images on a larger sheet (sized 11×17 inch, for example). These images must be separated into separate pages of appropriate size. The manipulating of sheets from the printer can entail forming secondary stacks and thereafter physically moving and directing the stacks through cutters and slitters to generate the final set of pages in the appropriate page order. This book block stack is then directed to the trimming and binding process by another set of manual tasks. Any defective pages or stacks are removed and dealt with by hand, typically requiring the reassembly of the defective stack with new replacement pages as appropriate.
Currently available electronic printers, such as the Indigo™ 5500 Digital Press, available from the Hewlett-Packard Company of Palo Alto, Calif., offer a wide range of print versatility at high levels of print quality. Such printers allow for the duplex (two-sided) printing of full color photo-quality images on a variety of paper types (matte, glossy, etc.), fed from sheets. These printers, and other of similar type, offer a high throughput speed (for example, currently up to approximately 70 pages per minute (ppm) for color print and up to approximately 270 ppm for monochrome print). Completed sheets, typically containing multiple, two-sided page images in appropriate sizes are stacked on an output stack that is subsequently divided into appropriate pages for binding in a finished book. A printing computer and associated software application(s), which interconnected with the print engine controller, organizes the order and location of images on each side of each sheet.
To fully take advantage of the speed and versatility of such electronic printers, the automation of the handling of output sheets is highly desirable. In general, it is desirable that the output sheets be automatically cut and slit to appropriate sizes and that this sizing process allow for the creation of accurate, full-bleed (e.g. marginless) pages that are ready to stack into completed books. The slitter arrangement is a significant element in the sizing of sheets. A common form of slitter provides a pair of rotating wheels that overlap in an impinging manner to form a scissor or shear surface. At the sheet is directed between these slitter wheels, it is cut along the upstream-to-downstream feed direction, thereby removing edge gutters and establishing a width dimension for the sheet. Slitters can be placed to provide inboard slits to the sheet that create a plurality of side-by-side sheets, each of a predetermined with. The widthwise dimension of the sheet is directly related to the lateral (widthwise) spacing between each pair of impinging slitter elements (wheels) and an adjacent pair of impinging slitter elements.
During setup, before a print job begins, slitter elements are typically moved along their associated drive shaft by hand to an appropriate location and then fixed in a position on the shaft using a set screw, clamp or other fastening mechanism that is manually secured. The placement of the slitter elements along the shaft (and resulting page width) is largely dependent on the operator's accuracy in setting up the slitter assembly. This requires time and may entail a plurality of test runs before the slitter is ready for runtime use. Automation of the positioning of slitter elements is somewhat challenging. The elements should be positively secured once they are in a desired position on the shaft, but should be free to move along the shaft during the adjustment process. Likewise, not all the slitter elements may be desired for a particular job, and the unused elements should be movable to a position where they do not interfere with the paper/sheet path. Moreover, the elements must be free to rotate during operation. These challenges can render ineffective certain types of adjustment mechanisms, such as a lead-screw that continually engages the slitter elements.
It is therefore desirable to provide a slitter adjustment mechanism that allows for free rotation of the slitter elements on their shaft, allows unused elements to be moved out of the paper/sheet path and that accurately adjusts the slitter elements to a desired position within the overall slitter assembly substantially free of manual contact by the operator.